9 binders cost $12.33. Which equation would help determine the cost of 14 binders?
Solution: There are several equations that could help determine the cost, each with a slightly different approach. Let $x$ represent the unknown cost of 14 binders. Since 14 binders cost $x$ , we have the following proportion: $\dfrac{14}{x}$ We can write the fact that 9 binders cost $12.33 as a proportion: $\dfrac{9}{\$12.33}$ The cost changes along with the number of binders purchased, and so the two proportions are equivalent. $\dfrac{14}{x} = \dfrac{9}{\$12.33}$